Cinthio, Magnus, Å sa Rydén Ahlgren, Jonas Bergkvist, Tomas Jansson, Hans W. Persson, and Kjell Lindström. Longitudinal movements and resulting shear strain of the arterial wall. Am J Physiol Heart Circ Physiol 291: H394 -H402, 2006. First published February 10, 2006 doi:10.1152/ajpheart.00988.2005.-There has been little interest in the longitudinal movement of the arterial wall. It has been assumed that this movement is negligible compared with the diameter change. Using a new high-resolution noninvasive ultrasonic method, we measured longitudinal movements and diameter change of the common carotid artery of 10 healthy humans. During the cardiac cycle, a distinct bidirectional longitudinal movement of the intimamedia complex could be observed in all the subjects. An antegrade longitudinal movement, i.e., in the direction of blood flow, in early systole [0.39 mm (SD 0.26)] was followed by a retrograde longitudinal movement, i.e., in the direction opposite blood flow [Ϫ0.52 mm (SD 0.27)], later in systole and a second antegrade longitudinal movement [0.41 mm (SD 0.33)] in diastole. The corresponding diameter change was 0.65 mm (SD 0.19). The adventitial region showed the same basic pattern of longitudinal movement; however, the magnitude of the movements was smaller than that of the intimamedia complex, thereby introducing shear strain and, thus, shear stress within the wall [maximum shear strain between the intima-media complex and the adventitial region was 0.36 rad (SD 0.26). These phenomena have not previously been described. Measurements were also performed on the abdominal aorta (n ϭ 3) and brachial (n ϭ 3) and popliteal (n ϭ 3) arteries. Our new information seems to be of fundamental importance for further study and evaluation of vascular biology and hemodynamics and, thus, for study of atherosclerosis and vascular diseases. carotid artery; vascular mechanics; arterial wall movements; shearing strain in arteries; vascular ultrasound IN CARDIOVASCULAR RESEARCH, radial movement of the arterial wall, i.e., diameter change, has been the subject of extensive research. Measurement of radial movements of arteries is an established tool in cardiovascular research (8,13,17,23), forming the basis for estimation of arterial wall stiffness. Increased stiffness of large central arteries has recently been shown to be an independent risk factor for cardiovascular mortality (4). In contrast to radial movements, there has been little interest in longitudinal movements of the arterial wall, i.e., along the vessel. It has been assumed that the longitudinal movement of the arterial wall during the cardiac cycle is negligible compared with the radial movement (21). Longitudinal movement of the arterial wall has not been studied, because, until the most recent improvements in ultrasound systems, it has not been possible to detect longitudinal movement in vivo. In the 1950s, using cinematographic observations of beads sutured to the surface of exposed vessels, Lawton and Greene (15) measured the longitudinal movement of the abd...

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A new non-invasive ultrasonic method for simultaneous measurements of longitudinal and radial arterial wall movements: first in vivo trial. General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal SummaryDuring recent years, the radial movement of the arterial wall has been extensively studied, and measurements of the radial movement are now an important tool in cardiovascular research for characterizing the mechanical properties of the arterial wall. In contrast, the longitudinal movement of vessels has gained little or no attention as it has been presumed that this movement is negligible. With modern high-resolution ultrasound, it can, however, be seen that the intima-media complex of the arterial wall moves not only in the radial direction, but also in the longitudinal direction during pulse-wave propagation. This paper describes a new non-invasive ultrasonic method that is able to measure simultaneously two dimensionally arterial vessel wall movements. The method is demonstrated in a limited in vivo trial. Results from the in vivo trial show that, apart from the well-known radial movement, there is a distinct longitudinal movement in the human common carotid artery with, in this case, the intima-media complex moving substantially as compared with the region of the tunica adventitia. Two-dimensional evaluation of the vessel-wall movements, taking not only the radial movement, but also the longitudinal movement into account, may provide novel information of importance in the evaluation of vesselwall function.

It has recently been demonstrated that superparamagnetic iron oxide nanoparticles can be used as magnetomotive ultrasound contrast agents. A time-varying external magnetic field acts to move the particles and, thus, the nanoparticle-laden tissue. However, the difficulty of distinguishing this magnetomotive motion from undesired movement induced in regions without nanoparticles or other motion artifacts has not been well reported. Using a high-frequency linear-array system, we found that displacements outside nanoparticle-laden regions can be similar in magnitude to those in regions containing nanoparticles. We also found that the displacement outside the nanoparticle regions had a phase shift of approximately π radians relative to that in the nanoparticle regions. To suppress signals arising from undesirable movements, we developed an algorithm based on quadrature detection and phase gating at the precise frequency of nanoparticle displacement. Thus, clutter at other frequencies can be filtered out, and the processed signal can be color-coded and superimposed on the B-mode image. The median signal-to-clutter ratio improvement using the proposed algorithm was 36 dB compared with simply summing the movement energy at all frequencies. This clutter rejection is a crucial step to move magnetomotive ultrasound imaging of nanoparticles toward in vivo investigations.